Biomedical subjects

R L Conhaim

Publications and source records attributed to R L Conhaim.

34 records · Page 2Linked to original sources

PubMed1993

Perfusion of alveolar septa in isolated rat lungs in zone 1.

The combination of high inflation and low vascular pressures in zone 1 lungs is assumed to collapse alveolar vessels, making them inaccessible to vascular liquid. To test this assumption, we perfused isolated rat lungs in zone 1 (n = 5) with fluorescent albumin solution (inflation pressure = 25 cmH2O, pulmonary arterial pressure = 10 cmH2O, left atrial pressure = 0 cmH2O; flow = 0.11 +/- 0.06 ml.100 g body wt-1 x min-1) and rapidly froze them. Histologically, 33 +/- 19% (SD) of alveolar septa fluoresced, demonstrating that the perfusate had not been excluded. However, we could not resolve whether the fluorescence originated in the septal microvascular lumen or in the adjacent perimicrovascular interstitial space. To address this issue, we perfused an additional lung with horseradish peroxidase (HRP) and examined it by transmission electron microscopy. HRP filled interstitial spaces around septal vessels and extraseptal alveolar corner vessels, but because the septal vascular lumina were too compressed, we were unable to determine whether they also contained HRP. Therefore we perfused two additional lungs with particles of colloidal gold (0.05 microns diam). Using transmission electron microscopy, we found gold particles in 15-25% of septal vascular lumina, demonstrating that septal vessels were at least partially accessible in zone 1. Our interpretations is that filtration in zone 1 may occur from septal vessels and extraseptal alveolar vessels. Furthermore, results of the HRP study suggest that the perimicrovascular interstitial space is less compressible than the septal vascular lumen.

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PubMed1992

A simplified two-pore filtration model explains the effects of hypoproteinemia on lung and soft tissue lymph flux in awake sheep.

We used a simplified two-pore filtration model to examine the effects of hypoproteinemia on lung and soft tissue lymph flux in awake sheep (n = 7). To induce hypoproteinemia, we subjected each animal to 3 days of batch plasmapheresis (6 units per day). Data were collected in near steady-state conditions, 15-18 hr following completion of the last plasmapheresis episode. At this time, plasma protein concentration had fallen by 34%, while lung and soft tissue lymph protein concentrations had fallen by 55 and 62%, respectively. Lung and soft tissue lymph flows increased 52 and 87%, respectively. The plasma-to-lymph osmotic pressure gradients for lung and soft tissue lymph were unchanged by protein depletion (soft tissue, 7.7 mm Hg; lung, 4.8 mm Hg). We applied these results to a heteropore model of the microvascular barrier that consisted of two types of pores: those which plasma proteins could not cross (sigma = 1) and those which proteins could cross without restriction (sigma = 0). We varied the proportion of small pores to large pores until the measured data fit a model in which the calculated microvascular hydrostatic pressures in normal and hypoproteinemic conditions were equal. This was based on the assumption that microvascular hydrostatic pressure did not change with plasma protein depletion. These conditions could be satisfied when the small pores accounted for 90% of total barrier porosity. According to the model, lymph flow increased in hypoproteinemia because of an increase in protein-free liquid flux through the large percentage of small pores; protein flux through the small percentage of large pores remained unchanged. The net result was an increase in lymph flow and a decrease in the lymph protein concentration. The model reproduced these changes even though the plasma-to-lymph osmotic pressure gradients were unchanged. We conclude that a simplified heteropore model can explain the effects of hypoproteinemia on lung and soft tissue lymph flux.

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PubMed1992

Effect of hyaluronidase on interstitial cuff and pressure response in liquid-inflated rabbit lung.

The sequential pattern of perivascular interstitial cuff growth was studied in liquid-inflated rabbit lungs. Degassed isolated lungs were immersed in a saline bath and inflated to 5 cmH2O transpulmonary pressure with a 3% albumin solution or 3% albumin solution containing hyaluronidase. After inflation times varying between 1 and 7 h, the lungs were frozen in liquid N2. From blocks cut from the frozen lungs, interstitial cuff cross-sectional area was measured as a function of vessel size. No cuffs were observed around vessels less than 0.1 mm diam. At all inflation times, only approximately 50% of vessels less than 0.5 mm diam had cuffs, whereas virtually all vessels greater than 0.5 mm diam had cuffs. Cuff-to-vessel area ratio increased with inflation time, reaching a maximum of 1.0-1.4 by 5 h. The time constant of cuff growth was 1 h for the albumin-inflated lungs and was independent of vessel size. The time constant was reduced by 60% in the hyaluronidase-inflated lungs. The time constant for the response in perivascular interstitial pressure measured by micropuncture near the lung hilum was 2.5 h for albumin-inflated lungs and 1.2 h for hyaluronidase-inflated lungs. Electrical analog models were used to fit the experimental data of cuff growth and to determine interstitial liquid resistance. Interstitial resistance for the albumin-inflated rabbit lungs was 2- and 24-fold greater than values estimated previously for sheep and dog lungs, respectively.

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PubMed1991

Pulmonary and systemic fluid filtration after continuous versus bolus interleukin-2 infusion.

Interleukin-2 has been widely investigated as adjuvant therapy for advanced cancer and is administered by either bolus or continuous infusion. We compared the effects of bolus and continuous interleukin-2 infusion on pulmonary (QL) and systemic microvascular fluid filtration in 11 adult sheep prepared with chronic lung and soft-tissue lymph fistulas. Interleukin-2 was administered as a bolus infusion (100,000 units/kg) every 8 hours for 3 days or as a continuous infusion at the same dose for 3 days. No significant changes in pulmonary hydrostatic pressures or pulmonary vascular resistance were noted after either bolus or continuous interleukin-2 infusion. However, significantly decreased (p less than or equal to 0.05) systemic vascular resistances were observed in both groups. QL increased steadily throughout the infusion period in both groups, peaking at three times baseline on the third infusion day. The plasma/interstitial protein clearance (QL X lymph/plasma protein ratio) rose similarly in both groups, indicating increased barrier permeability. Increased lymphocyte clearance into lung lymph occurred by day 3 but was not associated with lymphocytic sequestration in the lung interstitium. We conclude that pulmonary and systemic microvascular fluid and protein flux exhibit similar changes after bolus or continuous interleukin-2 infusion. These changes are associated with increased clearance of lymphocytes into lung lymph that are not sequestered in the pulmonary interstitium after infusions of shorter duration.

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PubMed1990

Pulmonary transvascular fluid filtration response to hypoproteinemia and Hespan infusion.

Management of major blood loss utilizing protein-free fluids for volume replacement frequently results in plasma protein depletion and plasma volume expansion. These factors can increase pulmonary transvascular fluid filtration which may lead to life-threatening pulmonary edema. We studied the combined effects of plasma protein depletion and plasma volume expansion on lung lymph flow (QL) in awake sheep prepared with chronic lung lymph fistulae. Animals were first chronically protein-depleted by batch plasmapheresis and then infused for 2 hr with either lactated Ringer's (Hypo/LR; n = 7) or 6% hydroxyethyl starch (Hespan) (Hypo/HES; n = 6). Control normoproteinemic animals (Norm/LR; n = 13) only received lactated Ringer's. Hypoproteinemia alone resulted in an average 2-fold increase in QL over normoproteinemic baseline levels (P less than or equal to 0.05). Infusion of LR into hypoproteinemic animals caused a 7.9-fold increase in QL (P less than or equal to 0.05). By comparison, HES infusion under similar hypoproteinemic conditions limited the increase in QL to 3.2-fold over baseline. We attributed this reduced rise in QL to Hespan's high oncotic pressure, which dramatically widened (by 4-5 mm Hg) the pulmonary-to-lymph oncotic pressure gradient. We did not observe this with LR infusion, or in previous studies employing intravenous infusion of plasma protein. Thus, the oncotic pressure of Hespan appears to significantly limit pulmonary fluid filtration during hypoproteinemia compared to LR. We do not believe that these effects are the results of any changes in microvascular porosity.

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PubMed1989

Sequence of interstitial liquid accumulation in liquid-inflated sheep lung lobes.

In the initial stages of pulmonary edema, liquid accumulates in the lung interstitium and appears as cuffs around pulmonary vessels. To determine the pattern, rate, and magnitude of cuff formation, we inflated sheep lungs to capacity with liquid (inflation pressure 19 cmH2O) for 3-300 min. After freezing the lobes in liquid N2, we measured perivascular cuff size and total perivascular volume in frozen blocks of each lobe and compared the results with previous measurements in dog lungs. Total cuff volume in sheep lungs reached a maximum value of 5% of air space volume, compared with 9% in dog lungs. In sheep lungs 94% of vessels greater than or equal to 0.5 mm diam and 16% of smaller vessels were surrounded by cuffs. In dog lungs these values were 99 and 47%, respectively. The ratio of cuff area to vessel area reached a maximum of 2.3 in sheep lungs and 3.4 in dog lungs. In an electrical analogue model designed to simulate cuff growth, estimated interstitial resistance to liquid flow was 6-15 times higher than similar estimates in dog lungs. These species differences might be the result of differences in the composition of the interstitial gel or to differences in the mechanical linkage between the lung parenchyma and vessel wall.

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PubMed1989

Airway level at which edema liquid enters the air space of isolated dog lungs.

To identify lung units associated with liquid leakage into the air space in high-pressure pulmonary edema, we perfused air-inflated dog lung lobes with albumin solution to fill the loose peribronchovascular interstitium. Next, we perfused the lobes for 90 s with fluorescent albumin solution then froze the lobes in liquid nitrogen. This procedure confined the fluorescent perfusate to the liquid flux pathway between the circulation and the air space and eliminated the previously filled peribronchovascular cuffs as a source of the fluorescence that entered the air space. We divided each frozen lobe into three horizontal layers and prepared fluorescence-microscopic sections of each layer. In the most apical layers where alveolar flooding was minimal, 10.6 +/- 21.0% (SD) of alveolar ducts were either fluorescence filled or air filled and continuous with fluorescence-filled alveoli. In the same layers, 11.0 +/- 19.0% of respiratory bronchioles were similarly labeled. No terminal bronchioles in these layers were fluorescence labeled. This suggested that the fluorescent albumin entered the air space across the epithelium of respiratory bronchioles, alveolar ducts, or their associated alveoli. To simulate an alternative explanation, i.e., that fluorescence first entered central airways then flowed into peripheral air spaces, we prepared two additional lobes that we first partially inflated with fluorescent albumin then filled to capacity with air. This pushed the fluorescent solution along the airways into the lung periphery. In these lobes the ciliary lining of bronchi and terminal bronchioles was fluorescence coated. By comparison, cilia in fluorescence-perfused lobes were not coated. We conclude that alveolar flooding in hydrostatic pulmonary edema occurs across the epithelium of alveolar ducts, respiratory bronchioles, or their associated alveoli.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1989

Effects of interleukin-2 on pulmonary and systemic transvascular fluid filtration.

Interleukin-2 (IL-2) therapy for patients with advanced cancer may be compromised by dose-limiting and life-threatening pulmonary and systemic edema. We studied the effects of bolus IL-2 infusion on lung and soft-tissue transvascular fluid and protein filtration in six sheep with chronic lung and soft-tissue lymphatic cannulation. Changes in lung (QL) and soft-tissue (QS) lymph flow were used as indicators of transvascular fluid filtration. A dose of 100,000 U/kg IL-2 was administered every 8 hours for 3 days. A significant increase (p less than or equal to 0.05) in both QL and QS was observed after each IL-2 infusion, with maximal flow occurring 2 to 3 hours after infusion. After 72 hours of IL-2 infusion, a fourfold maximal increase in QL occurred, which recovered to near-baseline values within 24 hours. Elevations in QL and QS were not associated with increases in pulmonary arterial or pulmonary arterial wedge pressures, but these elevations were associated with significant (p less than or equal to 0.05) increases in cardiac output (7.7 +/- 0.5 to 11.4 +/- 0.4 L/min) and a consistent decrease in systemic vascular resistance. A significant increase in lung lymph/plasma protein ratio (0.49 +/- 0.06 to 0.93 +/- 0.04 for albumin) revealed a marked increase in pulmonary microvascular porosity. This change, however, was not observed in the systemic microcirculation. Serum concentrations of tumor necrosis factor did not increase with the observed changes in pulmonary microvascular porosity. We conclude that IL-2 increases both pulmonary and systemic microvascular fluid flux. In addition, there is a marked increase in pulmonary, but not systemic, protein permeability that is not a consequence of changes mediated by tumor necrosis factor.

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PubMed1988

Equivalent pore estimate for the alveolar-airway barrier in isolated dog lung.

In high-pressure pulmonary edema, lung interstitial and air space edema liquids have equal protein concentrations (Am. J. Physiol. 231: 1466, 1976). This suggests that the alveolar-airway barrier separating the air and interstitial spaces is relatively unrestrictive, even without apparent epithelial injury. To estimate the equivalent pore population of the alveolar-airway barrier we inflated each of 18 isolated dog lung lobes for 1 h with a solution of colored tracer of uniform radius. Tracer radii ranged from 1.3 to 405 nm. After freezing the lobes in liquid N2, we measured interstitial tracer concentrations in frozen perivascular cuffs or in samples thawed after dissection from frozen cuffs. Relative to the concentrations instilled, interstitial concentrations ranged from 0.34 for the smallest particles (1.3 and 3.5 nm radius) to zero for particles with radii of 405 nm. From the results we designed a pore model of the alveolar-airway barrier to reproduce the concentrations we measured. No single-pore model could be obtained, although a three-pore model fit the data well. The model results predict that pores with radii of 1, 40, and 400 nm would account for 68, 30, and 2% of total liquid flux, respectively. The majority of liquid flux (68%) would occur through passageways smaller than the smallest tracer we used (1.3 nm radius). We believe the alveolar-airway barrier consists not only of tight intercellular junctions that allow passage of only water and electrolytes but also of a smaller number of large leaks that allow passage of particles up to nearly 400 nm in radius.

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PubMed1987

Pulmonary interstitial resistance.

The mechanical properties of the perivascular interstitium surrounding large pulmonary blood vessels are defined in terms of interstitial fluid pressure, interstitial compliance, and interstitial hydraulic resistance. Interstitial pressure is one of the main forces which determine liquid filtration across the microvascular barrier. Interstitial compliance is a measure of the ability of the interstitium to swell with hydration which increases interstitial pressure and reduces the filtration rate. Interstitial pressure and compliance are functions of the elastic properties of the surrounding lung parenchyma and the vessel wall. Solid continuum mechanics are used to describe the behavior of the lung parenchyma. The transport properties of the interstitium are described in terms of a porous material whose fluid resistance is determined by a permeability constant. The dynamics of interstitial fluid are governed by the coupling of the flow with the elastic environment. An electrical analog model is developed to predict the growth of interstitial fluid cuffs during edema formation.

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PubMed1987

Micropuncture measurement of alveolar liquid pressure in excised dog lung lobes.

We have investigated the mechanism of alveolar liquid filling in pulmonary edema. We excised, degassed, and intrabronchially filled 14 dog lung lobes from nine dogs with 75, 150, 225, or 350 ml of 5% albumin solution, and then air inflated the lobes to a constant airway pressure of 25 cmH2O. By use of micropipettes, we punctured subpleural alveoli to measure alveolar liquid pressure by the servo-null technique. Alveolar liquid pressure was constant in all lobes despite differences in lobe liquid volume and averaged 10.6 +/- 1.3 cmH2O. Thus, in all lobes a constant pressure drop of 14.4 cmH2O existed from airway to alveolar liquid across the air-liquid interface. We attribute this finding, on the basis of the Laplace equation, to an air-liquid interface of constant radius in all the lobes. In fact, we calculated from the Laplace equation an air-liquid interface radius which equalled morphological estimates of alveolar radius. We conclude that in the steady state, alveoli that contained liquid have a constant radius of curvature of the air-liquid interface possibly because they are always completely liquid filled.

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PubMed1986

Sequence of perivascular liquid accumulation in liquid-inflated dog lung lobes.

The peribronchovascular interstitium of the lung is a potential space that expands in pulmonary edema with the formation of large liquid cuffs. To study the time course of cuff formation we inflated nine isolated dog lung lobes with liquid to total lung capacity, rapidly froze them in liquid N2 after inflation periods of 1-300 min, then photographed 20 blocks of each lobe at X3 magnification. From the photographs we measured the ratio of cuff area to vessel area for arteries and veins of 0.05-8 mm diam. We found that the cuff-to-vessel area ratio attained a maximum value of 3-4, which was independent of vessel size. However, the first cuffs to reach maximum size were those around vessels of 0.1-0.5 mm diam, whereas cuffs around larger vessels filled more slowly. No cuffs were visible around vessels smaller than 0.1 mm diam. After 45 min cuffs had formed around 99% of all vessels larger than 0.5 mm diam but had formed around only 38% of veins and 91% of arteries of smaller diameter. We simulated the observed rate and pattern of cuff growth using electrical analog models. The filling pattern and model analyses suggest that liquid entered the interstitium from an air space site associated with arteries of approximately 0.1-1.0 mm diam, spread to adjacent sites, and eventually reached the lobe hilum. The estimated perivascular interstitial flow resistance decreased approximately 100-fold with cuff expansion.

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PubMed1986

Growth rate of perivascular cuffs in liquid-inflated dog lung lobes.

In the early stages of pulmonary edema, excess liquid leaving the pulmonary exchange vessels accumulates in the peribronchovascular interstitium where it forms large peribronchovascular cuffs. The peribronchovascular interstitium therefore acts as a reservoir to protect the air spaces from alveolar flooding. The rate of liquid accumulation and the liquid storage capacity of the cuffs determine how quickly alveolar flooding is likely to follow once edema formation has begun. To measure the rate and capacity of interstitial filling we inflated 11 isolated degassed dog lung lobes with liquid to an inflation pressure of 14 cmH2O (total lung capacity) for 1-300 min, then froze the lobes in liquid N2. We made photographs of 20 randomly selected 12 X 8-mm cross sections from each lobe and measured cuff volume from the photographs by point-counting. We found that cuff volume increased from 2.2% of air-space volume after 1 min of inflation to 9.3% after 300 min. To measure the driving pressure responsible for cuff formation we used micropipettes to measure subpleural interstitial liquid pressure at the hilum of three additional lobes. With liquid inflation pressure set to 14 cmH2O interstitial pressure rose exponentially to 11.5 cmH2O. Interstitial compliance calculated from our volume and pressure measurements equaled 0.09 ml X cmH2O-1 X g wet wt-1, a value similar to that measured in air-inflated lungs. Goldberg [Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H189-H198, 1980] has likened interstitial filling to the charging of a capacitor, a process that follows a monoexponential time course.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

Effect of lung inflation on alveolar-airway barrier protein permeability in dog lung.

To determine the leakiness to protein of the barrier that separates the air space and interstitial compartment of the lung, we measured perivascular interstitial fluid cuff protein concentration and volume in 10 isolated and 9 intact closed-chest dog lung lobes, which we degassed and inflated to 25, 50, 75, or 100% of capacity with 5% bovine serum albumin labeled with Evans blue dye. After 1 h we froze the lobes in liquid N2 and made color transparencies of 20 randomly selected frozen samples of each lobe. We measured Evans blue dye-albumin concentrations from absorption by cuff images of a 50-micron-diam red (lambda = 620 nm) microspot. We measured absolute cuff volume (ml/g dry lung) by point counting on the transparencies. Using specific Evans blue-albumin fluorescence we determined that the dye was protein bound in airways and cuffs. Cuff protein concentration averaged 37% of instillate concentration and did not vary with inflation volume or between isolated and intact lobes. Cuff volume was 3.4 ml/g dry lung at total lung capacity in both isolated and intact lobes. We conclude that at some point the barrier is permeable to albumin as well as liquid at all lung volumes in dogs and that the protein sieving properties of the barrier do not change with lung expansion over the range examined. The liquid storage capacity of the cuffs can increase as much as 20-fold between low and high lung volumes.

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PubMed1981

Rapid-freezing transmural cardiac biopsy drill.

We have built a transmural cardiac biopsy drill that uses an air turbine (10,000 rpm) to turn a stainless steel bore of either 2.0 or 4.5 mm diam. Vacuum draws the cut biopsies through the drill into isopentane chilled to -150 degrees C with liquid nitrogen. The steel bores cut through the beating canine left ventricular free wall in 0.14 +/- 0.04 (SD) permitting sampling in discrete portions of the cardiac cycle. Small and large biopsies traverse the drill in 0.48 +/- 0.19 and 0.15 +/- 0.04 s, respectively. Large biopsies freeze in 1.46 +/- 0.73 s, whereas small biopsies are calculated to freeze in 0.28 s. Average biopsy weights are 34 +/- 14 and 180 +/- 71 mg. Left ventricular myocardial blood flow measured with radionuclide-labeled microspheres showed that muscle plugs sutured into wound sites of 4.5-mm-diam biopsies cause a 30% reduction in myocardial blood flow within 0.5 cm of the biopsy site. Light microscopy shows normal cardiac muscle with little damage from drill rotation.

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PubMed1980

Reflection spectrophotometric measurement of O2 uptake in pulmonary arterioles of cats.

We have attempted to determine both experimentally and theoretically whether a significant quantity of oxygen enters the pulmonary blood before it reaches the alveolar wall capillaries. We built a microspectrophotometer that allowed us to record oxyhemoglobin saturation values with light reflected from transected frozen pulmonary arteries as small as 100 microns in diameter. We prepared anesthetized cats to provide optimal conditions for precapillary oxygenation, quickly froze their lungs with chilled liquid propane, and removed these lungs. We examined lung cross sections with the microspectrophotometer and recorded data indicating the presence of precapillary oxygenation. These data did not tell us how much this process normally contributes to total lung oxygenation because propane did not freeze the lungs fast enough to capture conditions exactly as they are in life. We therefore made several calculations to estimate the extent of precapillary oxygenation using available data on pulmonary arterial geometry and diffusing capacity. We concluded that pulmonary arterial blood may be as much as 15% oxygenated by this process at rest and as much as 100% during oxygen breathing.

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